Oil sand is essentially a matrix of bitumen, mineral matter and water. The bitumen component of oil sand consists of viscous hydrocarbons which behave much like a solid at normal in situ temperatures and which act as a binder for the other components of the oil sand matrix. The mineral matter component of oil sand typically consists largely of sand, but may also include rock, silt and clay. Sand and rock are considered to be coarse mineral matter, while clay and silt are considered to be fine mineral matter, where fines are defined as mineral matter having a particular size of less than 44 microns. The water component of oil sand consists essentially of a film of connate water surrounding the sand in the oil sand matrix, and may also contain particles of fine mineral matter within it.
A typical deposit of oil sand will contain about 10% to 12% bitumen and about 3% to 6% water, with the remainder of the oil sand being made up of solid mineral matter particles. Typically the mineral matter component in oil sand will contain about 14% to 20% fines, measured by weight of total mineral matter contained in the deposit, but the amount of fines may increase to about 30% or more for poorer quality deposits. Oil sand extracted from the Athabasca area near Fort McMurray, Alberta, Canada, averages about 11% bitumen, 5% water and 84% mineral matter, with about 15% to 20% of the mineral matter being made up of fines.
Oil sand deposits are mined for the purpose of extracting bitumen from the oil sand, which bitumen is then upgraded to synthetic crude oil. Accordingly, various processes have been developed for extracting the bitumen from the oil sand.
For instance, conventionally, a “hot water process” is used for extracting bitumen from oil sand in which both aggressive thermal action and aggressive mechanical action are used to liberate and separate bitumen from the oil sand. The hot water process is a three step process. First, the oil sand is conditioned by mixing it with hot water at about 95° Celsius and steam in a conditioning vessel which vigorously agitates the resulting slurry in order to completely disintegrate the oil sand. Second, once the disintegration is complete, the slurry undergoes a primary separation process. The primary separation process separates the slurry by allowing the sand and rock to settle out, and the bitumen, having air entrained within it, floats to the top of the slurry and is withdrawn as a bitumen froth. Third, the remainder of the slurry, which is referred to as the middlings, is then treated further or scavenged by froth flotation techniques to recover bitumen that did not float to the top of the slurry during the primary separation process. In this case, the bitumen recovered from the middlings may be returned to the primary separation process to form or comprise a portion of the bitumen froth.
Various attempts have been made to improve upon the hot water process, such as: Canadian Patent No. 1,085,761 issued on Sep. 16, 1980 to Rendall; U.S. Pat. No. 4,512,956 issued on Apr. 23, 1985 to Robinson et al; U.S. Pat. No. 4,533,459 issued on Aug. 6, 1985 to Dente et al; U.S. Pat. No. 4,414,117 issued on Nov. 8, 1983 to Yong et al; and U.S. Pat. No. 4,225,433 issued Sep. 30, 1980 to Liu et al.
Further, Canadian Patent Application No. 2,030,934 published on May 28, 1992 by Strand and Canadian Patent Application No. 2,124,199 published on Jun. 11, 1992 by Strand, both describe an extraction apparatus and process employing a countercurrent separator vessel in which oil sand is gently rolled from one end to the other by a spiral ribbon and mixer elements while hot water, defined as having a temperature of about 50° Celsius, circulates in the opposite direction. Two streams are then removed from opposite ends of the separator vessel. One stream contains coarse mineral matter and some water, while the other stream contains a bitumen froth comprised of bitumen and dispersed fine mineral matter.
As well, Canadian Patent No. 2,123,076 issued Nov. 17, 1998 to Strand et. al. utilizes the countercurrent separator vessel of the previously noted Canadian Patent Applications in the performance of an improved oil sand extraction process. Specifically, Strand et. al. describes an overall method for processing lumps of oil sand containing bitumen to produce a bitumen product and non segregating tailings of a solid material and a sludge. The method includes depositing the lumps of oil sand into a bath of warm water. The lumps are then conditioned by gently contacting them with the warm water to liberate and separate bitumen from the oil sand while minimizing the dispersal into the bath of fine material contained in the oil sand. The conditioning step is preferably performed utilizing the previously described countercurrent separator vessel.
Following conditioning, the solid material remaining after the liberation and separation of the bitumen from the oil sand is removed from the bath and collected for further processing. The bitumen froth, comprised of the warm water containing bitumen and dispersed fine material, is also removed from the bath and collected for further processing.
In each of the previously described bitumen recovery processes, a primary separation process, being the first or initial separation process, is performed on a slurry comprised of oil sand and water in order to separate an amount of the coarse mineral matter from the bitumen and dispersed fine mineral matter in the oil sand. Thus, as indicated, this primary separation process produces a bitumen froth comprised of bitumen, water and dispersed fine mineral matter.
Further, in each of the described processes, in order to produce a desired bitumen product from the bitumen froth, the bitumen froth is typically subjected to further processing. In particular, the bitumen froth typically undergoes one or more further or subsequent separation processes in order to further separate the bitumen in the bitumen froth from the fine mineral matter.
For instance, referring to Canadian Patent No. 2,123,076 to Strand et. al., the bitumen froth produced by the primary separation process is subsequently conducted through a number of further separation vessels in sequence. First, the bitumen froth is conducted to a conventional gravity froth separator. Specifically, the bitumen is sufficiently aerated by gas inclusions or entrained air as it leaves the primary separation vessel to float to the top of the froth separator, where it may be removed and collected. The underflow from the froth separator is then conducted to a conventional froth flotation cell. The conventional froth flotation cell aerates and mechanically agitates the underflow from the froth separator. Then, the overflow from the conventional froth flotation cell is conducted to a further conventional gravity froth separator, as described previously.
The amount of bitumen separated within a conventional gravity froth separator is largely dependent upon the degree of aeration of the bitumen entering the separator. Further, although a conventional froth flotation cell aerates the bitumen within the bitumen froth, the separation process also requires the mechanical agitation of the bitumen froth. The need to mechanically agitate the bitumen froth may render the process less energy efficient and require more maintenance of the moving parts, as compared to other separation vessels.
Thus, there is a need for an improved bitumen recovery process, and specifically, for an improved process for recovering a bitumen product from a bitumen froth produced in a primary separation process from a slurry comprising oil sand and water. Preferably, the process is relatively energy and cost efficient and produces a bitumen product having desirable characteristics or qualities, as compared with known bitumen recovery processes.